The invention concerns brush holders and brush holder subassemblies and their electrical connection, particularly for small motors of the type typically used in portable tools and domestic appliances.
Given the high production volumes and strong competition in the portable tool and appliance markets, economical design is essential for profitability. Design efforts to simplify and eliminate parts and to facilitate automation of assembly are patentially very rewarding. Brush holder design and arrangement, the subject matter of the present invention, has been included in these cost saving design activities. For example, U.S. Pat. Nos. 4,613,781 Sanders, and 4,498,230 Harris, sharing a common assignee with the present invention, both disclose brush holders of simple rectangular shape formed from a stamped flat pattern of sheet material and including an integral terminal for direct plug-in connection of the brush holder to other motor elements. U.S. Pat. No. 4,056,749 Carlson discloses a brush holder of similar construction supported by a motor end bracket and oriented so that in assembly a single brush terminal, extending axially, may be inserted directly into a fixed terminal of a terminal board on an end of the stator assembly of the motor. Electrical connection from a field winding to the brush is thus completed without the need for a jumper or additional terminals, simplifying assembly and facilitating its automation.
In the known simple formed sheet metal brush holder designs it is typical for the single terminal to be "close coupled" to the sleeve of the brush holder and, for strength and stability reasons, to be of limited length. The simple form of these brush holder designs largely predetermines and limits the disposition of the terminal relative to the brush holder sleeve and also its reach from the sleeve. This, in turn, limits the adaptability of the design concept in for example, motor configurations where direct plug-in connection of brush to field, by way of the brush holder, is desired and the axial spacing between field and brush is relatively great. And these simple brush holder designs are not, for example, obviously adaptable to more complex motors which may require two connections to each brush, for example in a dynamically braked motor using a dedicated secondary winding for the braking mode.